This invention relates to an improved hydraulic fracturing method for fracturing an unconsolidated zone in a subterranean formation by fracturing a nearby consolidated zone to form a fracture, which extends into the unconsolidated zone. This invention further relates to a method for producing fluids from an unconsolidated subterranean zone via a fracture extending from the unconsolidated zone through a consolidated zone to a wellbore.
Fracturing techniques for increasing the productivity of oil wells and the like penetrating subterranean formations is well known. Hydraulic fracturing can be accomplished from either uncased or cased wellbores, although more commonly fracturing is accomplished from cased wellbores through perforations in a casing in the wellbore. Such casings are typically cemented in place and prevent the movement of fluids upwardly or downwardly in the annular space between the inside of the wellbore and the outside of the casing. Such fracturing is accomplished by the use of high pressure pumping of fluids which may comprise a pad which is generally a non-proppant laden volume of fluid at a pressure above the rock parting pressure to cause a crack to propagate from the perforated interval and grow until it reaches a barrier zone. This pad is typically followed by a proppant slurry in stages. The proppant slurry typically comprises a proppant-laden fluid, which increases in proppant concentration near the end of the job. The proppant can be substantially any suitable hard particulate material. Some typical materials are sand, resin products, ceramics, small steel balls and the like. A wide variety of proppant materials are well known to the art. Further the proppant materials may be coated with resins or other tacky or adhesive materials to cause the proppant particles to adhere to each other to form a porous channel in the fracture once formed. Such fracturing treatments are conventional and are widely used in the art.
Many such fractures are created in consolidated formations to create a flow path in the formation in the area of the fracture. The term xe2x80x9cconsolidatedxe2x80x9d as used herein refers to formations or zones in formations wherein the materials comprising the formation are sufficiently solid and bound so that they do not move into the wellbore with produced fluids. By contrast, unconsolidated formations as used herein refers to formations or zones wherein the particulate materials comprising the formation are loosely associated and are produced into the wellbore with produced fluids. The discussion of consolidated/unconsolidated formations above refers to zones in a broader subterranean formation which contains the oil or gas bearing or other zone or zones of interest.
Such fracturing techniques are well known to those skilled in the art, particularly for use with consolidated formations. When unconsolidated formations are fractured, several difficulties are encountered. First, the fracture is difficult to complete since the unconsolidated formations readily collapse into the fracture when the pressure is removed. To overcome this difficulty, proppants have been used and proppants coated with an adhesive or tacky material have been used in an attempt to maintain an open flow pathway in the unconsolidated formation after pumping is stopped.
Even with such techniques, it has been found that substantial quantities of finely divided particulate material from the unconsolidated formations or zones are produced back into the wellbore through the fracture. This can result in a number of problems varying from plugging the fracture to filling the wellbore below the perforations through which the fracture was completed to shortening the life of pumping equipment and the like. Tile production of finely divided particulates from such fractured unconsolidated zones has been aggravated by the jetting action of the fracturing fluid into the fracture area through the perforations which tends to fluidize the formation in the vicinity of the wellbore and the fracture to some extent. As a result, techniques such as the use of adhesive or tacky proppants have been used, gravel packs have been used in the well to prevent the production of finely divided particulates into the wellbore and the like. Most of these techniques are relatively expensive and in many instances are of limited effectiveness. It is much more desirable if the production of finely divided particulate materials from the unconsolidated formation can be avoided completely.
Accordingly, a continuing effort has been directed to the development of improved fracturing methods and improved production methods which achieve the production of fluids from a fractured unconsolidated subterranean formation without the production of finely divided particulates from the unconsolidated formation.
According to the present invention, an indirect hydraulic fracturing method is provided for fracturing an unconsolidated zone in a subterranean formation comprising the unconsolidated zone and at least one consolidated zone positioned near the unconsolidated zone wherein the subterranean formation is penetrated by a cased wellbore by perforating a casing in the cased wellbore in a consolidated zone near the unconsolidated zone; and, fracturing the consolidated zone to form a fracture extending into the consolidated zone and from the consolidated zone into the unconsolidated zone.
The present invention further comprises a method for restricting the production of finely divided particulates from a fractured unconsolidated zone in a subterranean formation, the subterranean formation comprising the unconsolidated zone and at least one consolidated zone near the unconsolidated zone, the subterranean zone being penetrated by a cased wellbore by: perforating a casing in the cased wellbore in a consolidate zone near the unconsolidated zone; fracturing the consolidated zone to form a fracture extending into the consolidated zone and from the consolidated zone into the unconsolidated zone; and, producing fluids through the cased wellbore from the unconsolidated zone through the fracture in the consolidated zone and the perforations in the casing in the cased wellbore.